1. Field of Invention
The instant invention relates to an apparatus for prestart oiling of any pressure-lubricated machine that experiences frequent periods of rest between intervals of operation.
2. Description of Prior Art
During normal operation of an internal combustion engine, vital engine parts are supplied with oil by a pressure lubricating system. Oil is drawn from a sump by a pump driven by the running engine. The pump forces oil under pressure via galleries throughout the engine to vital bearing surfaces including the crankshaft, connecting rod, and cam bearings, and to the valve train.
Start-up of the engine inherently involves a period of inadequate lubrication. When an engine is shutdown after an interval of operation, oil drains from the lubricating system including, to varying degrees, the bearing surfaces, oil galleries, pump, filter, and possibly an oil cooler. Upon restarting, the engine cranks and then may run for several seconds before the lubricating system refills and oil is again supplied to the bearing surfaces. Higher operating temperatures at shutdown and longer intervals of rest increase the degree of drainage and the time required to reinstate proper lubrication.
It is well recognized that severe wear can occur during the repeated cold starts to which internal combustion engines are typically subjected. In addition to aggravated normal frictional wear as a result of inadequate lubrication, very harmful scoring of the bearing surfaces can occur. It is generally acknowledged that well over half of all bearing wear may occur as a result of cold starts.
Numerous prior art patents address this problem by the provision of a prestart oiling device. The majority of these employ an accumulator to store oil as well as the energy to deliver the oil to the engine. Prestart oiling is generally implemented by a solenoid valve, which is interposed in a conduit between the accumulator and the engine. The normally closed valve is opened shortly before or coincident with the starting sequence. Then during running operation, the accumulator is recharged from the engine's pressure lubricating system.
Several of the prior inventions utilize an accumulator in which air and oil are in direct contact. A problem with this type of accumulator is that the oil absorbs the pressurized air. Half, or even more, of the air can be absorbed within a few weeks. Thus, periodic maintenance to replenish the energy-storing air is a major disadvantage of this type of accumulator.
Other prior inventions incorporate various components to separate a portion of the accumulator as an air chamber without an oil interface. These components include flexible membranes and bladders, diaphragms with springs, and pistons with seals. Although these designs may overcome the air absorption problem, other disadvantages are inherent. Membranes, bladders, and diaphragms are subject to cracking and rupture. Piston designs tend to be costly to manufacture, and wear and leakage may dictate periodic maintenance.
Other disadvantages of prior inventions involve the means of controlling oil flow between engine and accumulator. Some designs comprise a single path conduit and a valve, installed in the conduit, energized to the open position while the engine's ignition is turned-on. Thus, the stored pressure in the accumulator tends to approximate the final operating oil pressure of the engine. As the operating pressure of a warm engine is much less than attained shortly after a cold start, much of the energy potentially available for prestart oiling is lost.
Some of the prior inventions use two separate paths: one with a solenoid valve to discharge oil from the accumulator, and one with a check valve to allow recharging of the accumulator. Among the disadvantages of this design is the increased potential for leaks due to additional connections in the conduit. Several prior inventions employ a valve design unique to the particular invention, and some are quite complex. Inexpensive, leakproof, reliable, durable, and proven solenoid valves are commercially available. Thus, use of a standard commercial valve offers important advantages.